648 proceedings of the academy of [dec, 



Fresh-water Shells. 

 MELANIID^. 



No specimen of this family was taken by the members of the 

 Stanford Expedition, the following species being represented by 

 specimens sent from the Goeldi Museum, 



Genus DOEYSSA H. and A. Adams. 



A rather extensive series of shells of this genus from the lower 

 Amazon and its tributaries seemed to unite the species inconspicua 

 Brot, transversa Lea, and niacapa Moricand in so puzzling a manner 

 that the writer referred the whole group to Dr. Pilsbry for critical 

 examination. Dr. Pilsbry kindly assorted the shells and wrote the 

 following notes and descriptions of new species and varieties, and he 

 has allowed their publication in this paper, 



''The Doryssas of the lower Amazon Valley are all, so far as authen- 

 tically localized specimens are available, specifically distinct from 

 those of Pernambuco and southward, and also from those of Guiana, 

 though obviously related to the latter, as would be expected from the 

 intercommunication of inland waters. Aside from certain species 

 described from 'South America,' 'Brazil,' or 'Amazon,' and as yet with- 

 out known local habitation, the following have been reported from the 

 lower Amazon Valley: 



"D. aquatilis (Reeve), Melania branca Reeve, and M. charpentieri 

 Reeve, Rio Branco. 



"D. macapa (Moricand), Macapd. 



"D. transversa (Lea). Guiana, Cuming coll., probably incorrect; 

 Amazon River, Brot. 



"D, hullata (Lea), Melania ventricosa Moricand, M. hatesii 

 Reeve. Macapd. 



"D. lumbricus (Reeve), Pard, 



" D. inconspicua Brot. Brazil. 



"An upper Amazon form, D. consolidata (Brug.), has been reported 

 from the Rio Branco, whether correctly or not is uncertain. Up to 

 this time, no species of Doryssa has been reported from the southern 

 affluents of the Amazon. 



"D. transversa, macapa, aquatilis, and inconspicua are modifications 

 of a single type of shell, and, until far more material is at hand, it 

 will not be possible to say whether they are to be regarded as so 

 many distinct species or as local races of one wide-spread species. 

 Each river seems to have its slightly individualized race or races, 

 but the localities are still so scattered that we have no adequate 

 knowledge of how much intergradation exists. 



